1. Field of the Invention
The present invention generally relates to an oil activated fuel injector and, more particularly, to a control valve used with an oil activated electronically or mechanically controlled fuel injector.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as xe2x80x9cgroovesxe2x80x9d) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
However, in such a conventional system, a response time between the injection cycles may be slow thus decreasing the efficiency of the fuel injector. This is mainly due to the slow movement of the control valve spool. More specifically, the slow movement of the control valve may result in a slow activation response time to begin the injection cycle. To remedy this inadequacy, additional pressurized working fluid may be needed; however, additional energy from the high pressure oil pump must be expanded in order to provide this additional working fluid. This leads to an inefficiency in the operations of the fuel injector, itself. Also, the working fluid at an end of an injection cycle may not be vented at an adequate response rate due to the slow movement of the control valve spool.
The present invention is directed to overcoming one or more of the problems as set forth above.
In a first aspect of the present invention, a control valve for a fuel injector is provided. The control valve has a valve body and a spool positioned within a bore of the valve body and slidable between a first position and a second position. A first bore is in fluid communication with a rail inlet of the fuel injector and a cross bore is positioned within the valve body and offset from the first bore. A groove is located about the spool and provides fluid communication between the cross bore and the first bore when the spool is in the first position and seals fluid communication between the first bore and the cross bore when the spool is in the second position.
In another aspect of the present invention, a fuel injector includes a fuel injector body having a bore disposed therein and an inlet port positioned within the fuel injector body. A working port provides fluid communication to an intensifier chamber of the fuel injector. A first spool is positioned within the bore of the fuel injector body and is slidable between a first position and a second position. The first spool includes a first leading edge and a second leading edge. A space is formed between the first leading edge and the fuel injector body when the first spool in the second position. A pressure chamber is associated with the first spool. A control valve is in communication with the pressure chamber and includes a valve body and a control spool positioned within a bore of the valve body and slidable between a first position and a second position. A first bore is in fluid communication with the pressure chamber and a cross bore is in fluid communication with ambient and positioned within the valve body and offset from the first bore. A groove is positioned about the control spool. In the first position of the control spool, the groove provides fluid communication between the cross bore and the first bore such that a pressure within the pressure chamber is substantially equal to a rail inlet pressure thereby permitting the first spool to move in the direction of the first position. This seals the space between the first leading edge and the fuel injector body and allows working fluid to flow from the inlet port to the intensifier chamber. In the second position of the control spool, the groove moves out of alignment with the cross bore thus inhibiting fluid flow between the pressure chamber and ambient such that the pressure within the pressure chamber increases to a higher pressure than the rail inlet pressure. This forces the first spool in the direction of the second position to form the space between the first leading edge and the fuel injector body and allowing working fluid to vent to ambient from the intensifier chamber.